The present invention relates to the attachment of electrically conductive adhesives to a circuit board which are intended to hold surface mounted devices, e.g., semiconductor devices (also termed "dies"), capacitors, resistors, etc. More particularly, it relates to a carrier film holding a series of adhesive patterns which are in the configuration desired for placement of the devices on the circuit board.
In copending U.S. application Ser. No. 519,936, now abandoned, entitled "Carrier Film with Conductive Adhesive for Dicing of Semiconductor Wafers", filed in the name of Joseph A. Aurichio, a carrier film having a series of conductive adhesive patterns thereon for dicing of semiconductor wafers into dies is described. It is contemplated that after the die had been cut from the wafer, the adhesive/die combination would be removed from the carrier film and then affixed to an appropriate circuit board. The carrier film product described in that application did not have the adhesive patterns in the ultimate configuration desired for a plurality of semiconductor devices on a circuit board so as to allow bonding of the carrier film to the circuit board with ultimate placement of the adhesive patterns in the desired configuration. The product was solely directed to a means for supporting semiconductor wafers for dicing in which the adhesive patterns on the film were not necessarily in any particular configuration which would bear a relationship to the position which the adhesive would need to have on the circuit board to allow proper placement of devices thereon.
Subsequently, in copending U.S. patent application Ser. No. 574,815, now abandoned, entitled "Conductive Die Attach Tape", also filed in the name of Joseph A. Aurichio, a conductive die attach tape is described. In such a tape product, a support tape contained a pattern of adhesive of a size and shape to support a semiconductor chip thereon. The individual chips would be positioned over the corresponding adhesive and contacted therewith. After contact between the chip and support film/adhesive composite had been made, the chip would be removed from the film with its adherent adhesive support. The individual chip/adhesive composite would then be placed into a suitable chip carrier on the desired circuit board and would be cured in an appropriate fashion prior to the wire bonding step. Once again, the product shown in this application is not intended to give a pre-patterned configuration of adhesive on a support film which could be later employed in transferring such a configuration of adhesive to a circuit board with the adhesive being in the appropriate places for attachment of a plurality of semiconductor devices to the circuit board.
In the assembly of circuit boards, especially hybrid circuit boards containing various surface mounted devices, e.g., semiconductor devices, in various locations, the devices are adhesively mounted directly to the circuit board substrate and are then appropriately bonded to the conductive circuit. Conventionally, the adhesive is conductive, e.g., a silver-filled epoxy, and is usually applied via either syringe or screen printing. Usually, the devices are automatically picked from a suitable device, i.e., a waffle pack, and are then placed onto the predeposited adhesive pattern with subsequent curing. Sometimes, other devices which have been soldered are already present on the substrate thereby causing problems in regard to screen printing of the adhesive because of the location of such soldered devices.
Therefore, a need exists for elimination of the conventional manner of using potentially difficult-to-handle epoxies which many times have short shelf lives and which often need to be kept frozen until use. Conventional procedures for applying adhesive mountings to circuit boards in the desired locations can involve wastage of wet adhesive which, due to improper handling and use, must then be discarded if not employed. There also is a need to eliminate the actual application for wet adhesive by the assembler and to provide a means of placing adhesive on the circuit board in the desired locations which is not easily amenable to conventional screen printing techniques.